Karl Landsteiner University of Health Sciences, Dr.-Karl-Dorrek-Straße 30, 3500 Krems an der Donau, Austria; Department of Neurosurgery, University Hospital St. Pölten, Dunant-Platz 1, 3100 St, Pölten, Austria; Cerebrovascular Research Group, Department of Neurosurgery, University Hospital St. Pölten, Dunant-Platz 1, 3100 St, Pölten, Austria. Electronic address: branko.popadic@stpoelten.lknoe.at.